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I think any of them would probably perform satisfactorily for that task.  When if comes to running 60 to 100 thousand miles a year with some pretty heavy loads and various terrain, I've had excellent results with the Duramax-Allison combination.  The earlier ones did have some frequent injector problems, but the guys I know running the later ones from '05 and up have not had many injector failures.  I think the warranty has been kicked up to 2oo K for the earlier ones.  The Allison 5 or 6 is almost bullet proof.  It may have happened, but I've never personally known anyone having a failure of the Allison tranny.  I've never had to be towed in any of the Duramax I've owned and had to limp back only twice.  Both times I limped in were due to a fuel filter clogging and both times I had been fueling at Love's truck stops.  I now change the fuel filter every 15,000 miles and if I can avoid it I don't stop at Love's.  Based on what has been written in some of the truck forums, the older Dodges with the manual transmission were plagued with tranny failures.  But the little Cummins 6 pak was as good as gold and I believe it routinely had better fuel mileage than the stock Duramax.  I don't know crap about the new bigger Cummins.  The old Power Stroke 7.3 always seemed to be a good performer and relatively durable and reliable with no significant failures up to about 200K miles.  After that, I've heard they really went down hill unless you did a complete rebuild.  I know a few guys running the newer Ford Power Strokes and most seem to like them, although I've also read that they were prone to break down for a variety of different reasons.  The new twin turbo must be a piece of crap, at least that is what I hear from every one I know that is running them.  A visit to the local Ford dealer usually finds a lot of them in with problems and at a very low mileage too.  But there will always be "brand loyalty" and a certain amount of bias among each of us.  My own experiences, the local dealer where I buy the trucks, and price have a significant influence on what I buy.  My bet is that any one of the top three diesels would perform well if they're maintained properly and treated okay.  I've often said that I wish someone would slap a beefed up little Cummins 6 pak in front of an Allison 6 speed, and I'd buy it.  I wouldn't care what flavor it was or how it looked...that would be a tough combination to beat.  And it may be coming soon!